From https://github.com/MarkEdmondson1234/ga-get-to-post/blob/master/main.py and blogpost http://markedmondson.me/e-mail-open-rate-tracking-with-google-analytics-measurement-protocol-demo

imageRequest.py

def getUniqueClientId(seed=''):
  """Function to create the cid from the parameter passed in. Change this as needed """
  if seed: random.seed(seed)

  ## make this so its always unique by referring to a set or using md5 or something
  theID = str(random.randint(1,9999)).zfill(4) + "-" + str(random.randint(1,9999)).zfill(4) + "-" + str(random.randint(1,9999)).zfill(4) + "-" + str(random.randint(1,9999)).zfill(4)
  return theID


class ImageRequest(blobstore_handlers.BlobstoreDownloadHandler):
  """The image that is in the email, and has a unique ID attached to it"""
  """This is called when the image is viewed, say in an email or another website"""
  def get(self):
    p = cgi.escape(self.request.get('p'))
    c = cgi.escape(self.request.get('c'))
    cid = cgi.escape(self.request.get('cid'))
    nohit = cgi.escape(self.request.get('nohit'))
    
    ## if it has the same seed, creates an id like xxxx-xxxx-xxxx-xxxx
    cid = getUniqueClientId(cid)
    ## construct the Measurement Protocol call
    ga_url_stem = "http://www.google-analytics.com/collect"
    ## refer to https://developers.google.com/analytics/devguides/collection/protocol/v1/devguide
    values = {'v' : 1,
              'tid' : 'UA-54019251-3', ## replace with your GA ID
              'cid' : cid}
    
    if p: ## make a pageview when people see the image
      values['t'] = 'pageview'
      values['dh'] = 'external_email'
      values['ec'] = 'email'
      values['ea'] = 'open'
    else: ## else make an event
      values['t'] = 'event'
      values['ec'] = 'email'
      values['ea'] = 'open'

    if c: ## put campaign info in the pageview
      values['el'] = c
      values['dp'] = '/vpv/email-view/' + c
    else: ## put campaign info in the event labels
      values['el'] = "campaign_name"
      values['dp'] = '/vpv/email-view'
    
    ### z is the cache buster
    values['z'] = str(random.randint(1,999999)).zfill(6)

    if not nohit: ## nohit=1 if you don't want to send hit to GA
      ### send the hit to Google as a POST
      data = urllib.urlencode(values)
      req = urllib2.Request(ga_url_stem, data)
      response = urllib2.urlopen(req)
      the_page = response.read()

    print values ## look in logs to see what was sent

    ### get the image upload previously done at /upload-image.html and stored in datastore
    pixel = Pixel.get_by_id("image")
    ### serve up image
    if pixel:
      img = blobstore.BlobInfo.get(pixel.img)
      self.send_blob(img)
    else:
      self.response.out.write("no image")